Control apparatus



Ma1 chI8,1941. F GIBBS HAL 2235,12

CONTROL APPARATUS Fiied Sept. 15, 193'? AIR SUPPLY 33 13 5s 66 mr' afiwfim 0104 9 31' 21 I: so

Frank c. Gibbs Karl Figienbqum INVENTORS ATTQRNEY I Patented Mar. 18, 1941 UNITED STATES PATENT OFFICE 2,235,150 CONTROL APPARATUS Application September 15, 1937, Serial No. 164,008

12 Claims.

This invention relates in general to automatic controls, and is more particularly concerned with automatic controls for controlling air conditioning apparatus.

5 In the heating and ventilating art, it has become common to heat and ventilate large spaces such as school rooms or auditoriums by devices known as unit ventilators. These unit ventilators usually consist of a casing enclosing a heating l element, and a fan for causing air to pass through the heating element and out into the space being heated. These ventilators are also provided with two air inlets, one inlet allowing air from the room (recirculated air) to pass into the casing,

15 and the other inlet allowing air from outside the building (fresh air) to flow into the casing. Usually some form of damper arrangement is provided for controlling the mixture of fresh air and recirculated air taken into the casing, and it has 20 become common to vary the mixture of fresh and recirculated air in accordance with temperature conditions within the space, in order to prevent overheating in mild weather and to avoid excessive heating loads in severe weather.

95 In many cases, a plurality of such unit ventilators are installed in a single room or space and both the heating elements and the fresh and recirculated air damper mechanism of all of the units are controlled by a single thermostat re- 30 sponsive to the temperature of the space being conditioned. While the specific sequence of operation of the heating elements and damper mechanism may take several forms, in general, the thermostat controls the heating element in a 35 manner to gradually place it'out of operation as the space temperature increases above a predetermined value, and controls the damper mechanism in a manner to increase the supply of fresh air as the space temperature increases.

40 Thus when the space temperature is too high, all fresh air will be supplied to the unit, and the heating element will be placed out of operation. As the space temperature falls, however, the heating element will be gradually placed in operation,

4-) and the supply of fresh air will be reduced. When the space temperature falls to a predetermined low value, the heating element will be in full operation, and the damper mechanism will be positioned so as to prevent any fresh air at all 50 from being supplied to the unit in order to avoid an excessive heating load.

In some localities, however, local statutes require that the fresh air supply shall not be reduced below a predetermined minimum when- 5 ever the space is occupied. It is thus necessary in installations in these localities to provide an arrangement for preventing the damper mecha nism from closing off the fresh air damper even though the temperature of the space may be too low. Such an arrangement alone, however, is not fully satisfactory, for it is desirable for economy reasons toclose off the fresh air supply when the space is not being occupied. It is therefore necessary to provide an arrangement'which limits the movement of the damper for maintain- 1o ing a minimum fresh air supply during periods of occupancy, and which permits the fresh air supply to be closed off during periods of nonoccupancy.

One manner in which this result has been achieved in the past has been by utilizing two separate motors for controlling the damper mechanism of each unit, one motor being under the control of the thermostat, and the other being manually controlled by a switch line, this second motor acting to prevent the damper mechanism from completely closing oil the fresh air supply when energized and to permit the first motor to completely control the damper mechanism when the second motor is deenergized. 26

While such arrangements are somewhat satisfactory in operation, they are not entirely desirable'for the reason that the provision of each unit with an extra motor materially increases thecost of the control equipment, where a large number 30 of units is being controlled.

It is therefore an object of our invention to provide a novel control arrangement for unit ventilator damper mechanism which utilizes but one damper motor for each unit and which permits said damper mechanism to be controlled from a thermostat in a manner to prevent the supply of fresh air from being reduced beyond a predetermined minimum by said thermostat during one period of time while permitting com- 40 plete closing ofi of the fresh air supply by the thermostat at other periods of time.

While the primary object of our invention is to provide a control system for unit ventilators, our invention is not limited to such apparatus. Other objects of our invention will become apparent from the following description and the appended claims.

For a full description of our invention, reference is made to the following detailed description and to the accompanying drawing, the single figure of s which shows in elevation a device embodying the principles of our invention and which shows diagrammatically the various elements forming a unit ventilator control system.

'2 and a fresh air inlet 4.

Referring to the drawing, reference character I indicates generall a unit ventilator which consists of a casing 2 having a recirculated air inlet The recirculated air inlet 2 may be provided with the usual grill I while the fresh air inlet 4 is in communication with an opening 6 through the wall of the space being heated. Located within the casing 2 is the usual fan 1 and an air fin type of heating coil 8. The flow of steam or other heating medium into the heating coil 2 may be controlled by a pneumatic control valve 9 of known construction. Above the heating element 9 is an outlet ID for allowing the heated ar to be discharged into the space being conditioned. As shown, the casing 2 is provided with inwardly extending baflies H and I2 which cooperate with a damper |2 pivoted at l4, for controlling the flow of fresh and recirculated air into the device. The damper -|3 is actuated by a suitable pneumatic damper motor I! which may be of any desired type. This damper motor is shown as comprising a bellows which is connected by a suitable link to the damper l2. Upon an increase in pressure within the bellows, said bellows will expand thereby causing movement of the damper I2 towards the baille thereby restricting the flow of recirculated air into the casing and increasing the flow '0! fresh air thereinto. Upon a decrease inpreasure within the bellows, the bellows will contract under the action of a spring It thus moving the damper |2 in a direction to increase the flow of recirculated air and to decrease the flow of fresh air.

Both the damper motor I! and the steam valve 9 may be controlled by means of a thermostat 2B which is responsive to the temperature of the space being heated by the unit ventilator 2. Also if desired, direct radiation asindicated at 2| may be provided for supplementing the heating effect of the unit ventilators, and this direct radiation may also be controlled by the thermostat 29. The thermostat 28 may be of any desired type and isshown herein diagrammatically as comprising a temperature responsive tube 22 within which is located a bleed port 22 cooperating with a flapper valve 24. The valve 24 may be actuated by a rod 25 formed of non-expansible material. It will be understood that as the temperature within the space increases, the tube 22 will increase in length, this causing an upward movement of the rod 25 thereby permitting the flapper valve 24 to approach the port 22. Upon a decrease in temperature, the opposite action will take place, namely, the valve 24 will be moved away from the bleed port 22. The bleed port 22 is connected through a restriction 26 to an air supply line 21-. The bleed port in addition is connected to a branch line 28, said branch line 28 including a portion 29 leading to the \mit heater valve 9 and a portion 29 which leads to the valve 2| for the direct radiation 2|. Both the valve 9 and the valve 2| are of the direct acting type, this type of valve being arranged to close on the steam supplied as the pressure applied hereto increases. The valve 2|, if desired-may be arranged to assume a wide open position when no air pressure is applied thereto, and to assume a fully closed position when the air pressure applied to said valve is raised to tour pounds per square inch. The unit heater valve 2, however, may be arranged so as to remain open until the air pressure applied thereto reaches six pounds and to become completely closed when the air pressure is raised to eleven pounds. r I

With this arrangement of the valves, they will operate sequentially. Thus when the space temperature is low enough to cause the bleed port valve to be wideopen (for instance 68 1".) no pressure will be applied to either steam valve and hence both steam valves will be wide open. As the space temperature increases to 68.5, however, the thermostat will bleed 01! less air thereby causing the branch line pressure to be increased to four pounds per Square inch which causes the valve 2| for the direct radiation to become closed. Upon further increase in temperature, the branch line pressure will be further increased which will begin closing oi! the unit heater valve when the branch line pressure has been increased above six pounds per square inch. It will be seen, therefore, that upon rise in room temperature the direct radiation is first cut oil and then the flow oi steam to the unit heater is gradually cut oil. The arrangement thus far described is common in the art and forms no part of our invention.

In accordance with our invention, the damper I2 is also controlled by the thermostat 24 and during periods of occupancy of this space. the fresh air damper i2 is prevented from completely shutting oi! the flow of fresh air, while during periods of non-occupancy the thermostat 24 is allowed to completely shut on the flow of fresh air into the space. In order to achieve this result, a relay generally indicated as 22 is provided. Relay 2! comprises an upper housing member 26 having an enlarged upper portion 21 and a reduced lower portion 22. The enlarged upper portion 21 is provided with a closure member 39 which is screw threaded into said portion 31 as shown. The closure member 29 is provided with an air passage 40 and is also provided with a screw threaded extension 4| which cooperates with a union nut 42 for securing a pipe 42 in communication with the air passage 42. The pipe 42 communicates with the branch line 22 as shown. The air passage 42 is enlarged at the lower end of the closure member 29 and is screw threaded to receive a nipple 44 which secures thereto an expansible cell 45 which is located within the enlarged portion 21 of the upper housing member 36. The expansible cell 44 abuts a plunger head 46 which is secured to a plunger 41 which leads through an intermediate connecting member 48 into a lower housing member 49. As shown, the intermediate connecting member 48 is screwed threaded to the upper housing member and into the lower housing member, and provides a support for a spring 52 which abuts against the lower side of a plunger head 46.

The lower housing member 49 is hollowed out to provide a chamber 5| which communicates with a smaller bored out portion 52. Member 49 is also provided with an air inlet opening 22 which communicates through a passage 54 in the member 49 with a coinciding passage 55 in the intermediate portion 42, this passage 55 leading inwardly to the plunger 41. The plunger guide in the intermediate member 48 isenlarged as at 56 to provide for air flow from the passage 55 around the plunger 41, into the chamber ll. Attached to the lower face of the intermediate connecting member 42 is a sealing bellows 21, this bellows being attached at its lower end .to a bellows head 52 which is sealed to the plunger 41. The bellows 51 and the bellows head 58, therefore, prevent leakage oi air from the enlarged passage 58 into the chamber 5|. The chamber Si is also provided with an. outlet passage 59 which communicates with an outlet connection 80.

The lower end of the plunger 51 is provided with a longitudinal bore 6| which communicates with a lateral bore Ola within the plunger 61. These bores provide a passage from the interior of the bellows 51 to the exterior thereof. The lower end of the plunger 41 is formed as a valve seat which cooperates with a double valve member 52 which is located within the passage 52. The lower end of the passage 52 is enlarged at to form a valve chamber having a. valve seat 5% which cooperates with a valve element 65 which forms the other element of the double valve member 62. shown, the chamber 83 is provided with a closure member 66 having a portion housing a spring 81 which urges the valve member 62 upwardly so that the valve element 65 engages the valve seat 64. The closure member 66 is also arranged to form part of a union connection including a union nut ,68 for connecting a pipe 68 into communication with the valve chamber 58. The pipe Gilmay be connected to the branch pipe 30. It will be seen, therefore, that both the pipe 43 and the pipe as are connected to the branch line from the thermostat 29.

Due to the action of the spring 50 in holding the plunger head 65 against the expansible cell 45, the plunger 5? will move longitudinally upon movements of the expansible cell 45 due to changes in pressure therein. The spring 50 is so designed relative to the area of the expansible cell 45 that when the air pressure within the expansible cell is below 5 lbs. per square inch, said spring will urge the plunger 41 upwardly a distance suflicient to disengage its end from the valve member 52 as shown. This will permit a flow of air from the inside of the sealing bellows 57 to the exterior thereof. Also at this time, the spring 61 will urge the valve member 62 upwardly for causing the portion 65 thereof to engage the valve seat. 64. when the pressure within the expansible cell 45 is increased above 5 lbs. per square inch, however, the expansible cell will cause movement of the plunger 41 against the action of the spring 59 sufiiclently to cause engagement of the lower end of passage Si with the valve member 62, this preventing fiow of air from the interior of the sealing bellows 51 to the exterior thereof, and also causing the valve portion 65 to be moved away from the valve seat 64.

The outlet connection Bil of the relay 35 is connected by a pipe Hi to the damper motor i5 located within the unit ventilator. The air inlet 53 for the relay 35 may be connected by a pipe ii to a three-way valve 12, this valve in turn being connected to the outlet of a pressure reducing valve I3 which is connected to the main air supply line as indicated. This pressure reducing valve 13 may be set to maintain five pounds per square inch pressure. The threeway valve 12 is of usual construction and is arranged so that it can connect the outlet of the pressure reducing valve to the inlet 53 of the relay or to disconnect the inlet 53 from the reducing valve and connect said air inlet to atmosphere.

' space temperature is-below 68 F., as indicated tioned to permit the flow of air at a pressure ci 7 prevents this air at live pounds Operation If desired, the damper motor i5 and the spring [6 may be so designed that when the pressure applied to the damper motor is below four pounds per square inch, the damper I3 will be held by the spring it against the baiile 42, thereby preventing any flow of fresh air into the speecheing heated. When, however, the pressure applied to motor i5 is raised above four pounds per square inch, the damper I! will be moved away from the baille l2 9. distance proportionate to the pressure applied, and when the pressure applied is raised to eight pounds per square inch,.the damper I; will engage the baiiie Ii thus preventing. any flow of recirculated air into the casing and permitting the device to take in all fresh air. i

7 With the parts in the position shown, the

by the flapper valve 24 being shifted away from the bleed port 23. There' is, therefore no pressure whatsoever in the branch line 28 and accordingly the unit heater valve 9 and the direct radiationvalve 3i willbe'wide open. Abe ,atthis time, the damper l3 would be positioned against the baflie I! to prevent any fresh air supply were it not for theaction of relay 85. Referring to the relay 35,"the; expansible'cell 45 is collapsed due to the lack of air pressure therein, this causing the lower end of plunger; 41 to disengage valve member '62, thereby per- I mitting the valve portion 65 to engage theseat? 64. .As shown, the three-way valve I2 is posiflve pounds per square inch from the reducing valve 13 through the pipe '1] toithe inlet 58 or relay 35. This air passes from inlet 53 through passages 54, 55, and 56 into the interior ,0! the sealing bellows 51, and from there flowsthrough the passages 6i and Sic. to the exterior of bellows and through passage 59 to theoutlet 55;"

of the relay, from which it iiowsthroughpipe iii to the damper motor l5. Airflat nvejpounasgl' pressure per square inch is thereiore beingl supek plied to the damper motor 15; and accordingly"; the damper I3 has assumed s 'position pcrmityj ting aminimum ireshair supply- 1f Therefore, even though the thermostat 20. would normally cause the damper i3 to be posltioncdior stop- 1: ping all fresh air supply, the relay 35 will act to cause the damper I 3 to be positioned for su plying a predetermined 'mini'mum amountbffl, fresh air to the space. At-lthlsgtime, it'shouldi be noted that valve portion io is fiengaging the.

at five pounds pressure through: pipefis-intothe" branch line from the thermostats v therefore prevents the five pounds pressureIWhich isQbg-fing supplied to the dampeifi'motor' irom'b'eing supplied to the steam valves QfIandSL-Iand' assure from t ematic-.2

being applied to the bleed port-o stat, thereby avoiding excessive throughsaid bleedport. I j If now should the space temperature beginris- I ing, the flapper valve. 24 oi'thejthermostat 28 will j be caused to approachthe'bleediport 23, which; causes a rising pressure within'the. thermostat branch line 28. Thusya's the temperaturerises 70 from 68 F. to 68.5F. the'branch line pressure will be increasedfrom zero to four pounds D square inch, which will'cause closing of the direct radiation control valve 3| without aiieoting N the unit ventilator valve 9, due to the fact that 7| valve 0 is adjusted so as to remain wide open until the branch line pressure rises above six pounds per square inch. As the space temperature continues to increase, and increases above five pounds per square inch. the expansible cell will expand suiiiciently to cause the end of plunger 41 to engage valve 2, thus closing the passage I and also causing the: valve portion to disen ge the valve seat It. This will permit the branch line pressure to how through pipe 6! past causes the branch line pressure to rise above five pounds per square inch, the relay 35 in response to this action willdisconnect the constant pressure supply from the damper motor and place the damper motor under the control of the thermostat 20.

When the space temperature rises further to,

for instance 69 R, the branch line pressure will be increased by the thermostat to six pounds per square inch, which will cause the damper motor I! to position the damper ii for, supplying equal quantities of fresh and recirculated air to the unit ventilator. At this time, the unit heater valve I will remain wide open. Upon further increase in space temperature, however, the valve 9 will be gradually closed and also the damper II will be positioned to supply increasing amounts of fresh airto the space. Thus, when the space temperature rises to 69.5 F'. the branch line pressure will be equal to eight pounds per square inch and the damper it will be'positioned against baille II, this causing all fresh air to be supplied to the space and also causing the steam supply valve 9 to be half-closed. Upon further rise in temperature above 69.5 F., the valve 9 will be gradually closed and will assume fully closed position when the air supply is increased to eleven pounds per square inch, as will occur when the space temperature rises to 70 F.

Upon falling temperature, it will be apparent that just the reverse action from the above described will take place. Thus, first the unit ventilator valve will be graduatingly opened to halfopen position while the damper l3 remains in position to supply all fresh air to the space. Upon .further fall in temperature, both the unit. ventilator valve 9 will be further opened, and the damper 13 will be graduatingly positioned to supply smaller and smaller quantities of fresh air to the space. As the temperature falls to such a value that the branch line pressure from the thermostat is reduced below five pounds, the relay 35 will cause the damper motor IE to be disconnected from the thermostat branch line and to be connected with the constant pressure supthe three-way valve 12 will be positionedior cutting off the supply of air at five pounds per square inch pressure to the relay, and for causing the pipe H to be opened to atmosphere. If at this time the thermostat branch line pressure is below five pounds per square inch, the lower end of plunger 41 will be disengaged from valve 02, thereby permitting the air to W from the damper motor I! through pipe ill, passage 59 and passages 8i and Bid into the interior of the sealing bellows 61, from which it flows through passages 56, 55, and 54 and pipe H to atmosphere. This will cause the damper II to be positioned for cutting oil? all supply of fresh air to the space. 'As the space temperature increases, the branch line pressure of the thermostat will be increased and when it increases above five pounds per square inch, the lower end of plunger 41 will engage valve 62 for preventing flow of air through passage BI and also the valve portion 65 will be disengaged from the valve seat 4 which permits the thermostat branch line pressure to be applied to the damper motor l5. Upon further increase in temperature, the thermostat branch line pressure will increase and consequently the pressure applied to the damper motor II will likewise increase for causing more fresh air to be supplied to the space. When the valve 12 is positioned for venting the pipe ll, therefore, the damper i3 instead of being controlled to maintain at least a minimum fresh air supply, is actually caused to close of! the fresh air supply when the space temperature is below a predetermined value. When, however, the space temperature is above a predetermined value, such as 68.53 the control of the damper i3 isagain returned to the thermostat 20. This arrangement provides for complete closing of the fresh air damper when the space temperature is too low and further provides for preventing overheating of the space by supplying fresh air there- From the foregoing description, it should be apparent that we have provided a novel control arrangement by which a fresh air damper may be controlled from a thermostat which also controls other controllers, our arrangement preventing the thermostat from completely closing the fresh air damper when the space isoccupied, and permitting the thermostat to completely close 0!! the fresh air supply when the space is unoccupied. Furthermore, by our invention only one damper motor is necessary for securing this result. While we have shown but one unit ventilator being controlled, it will be understood that as many unit ventilators as desired may be controlled by the thermostat 20 and the relay 35, these additional ventilators being connected to the pipes 14 and 15, Also, while we have shown an arrangement in which the control of the fresh air damper is returned to the thermostat during periods of unoccupancy when the space temperature increases above a predetermined value, it will be understood that ii desired, suitable valves may be employed for causing said damper to completely close oil the fresh air supply at such times. Furthermore while in describing our invention, we have stated a specific sequence of operation of the steam valves and the damper, it will be understood that the particular sequence may be modia ing said controller to be positioned at least a predetermined distance from one limit 0! its move- 2,285,160 application and may be used forcontrolling many other types of equipment. As many modifications of our disclosure which are within the scope and spirit of our invention will be obvious to those skilled in the art, we desire to'be limited only by the scope of the appended claims as construed in the light of the prior art.

We claim as our invention: 1.'In a system of the class described, in combination, a controller movable from one position dition responsive means from said motor means when the value of the condition to which said condition responsive device responds varies beyond a predetermined value. I

2. In a pneumatic control system, in combina- 1 tion, a controller movable from one position to another, pressure actuated motor means for said controller operable to position said controller in accordance with the pressure applied to said motor means, a condition responsive device for varying the pressure applied to said motor means upon change in value of the condition to which said device is responsive to thereby cause the position of said controller to be variedin accordance with said condition, means operable to control the pressure to said'motor means independently of said condition responsive device for causment, and means controlled by said condition responsive means for connecting either said condition responsive means or said last recited means to said motor means, v

3. In a pneumatic control system, in combination, a controller movable from one position to another, pressure actuated motor means for said controller operable to position said controller in accordance with the pressure appliedto said motor means through a control line, a condition re sponsive device for varying the pressure in said control line upon change in value of the'condition to which said device is responsive to thereby cause the position of said controller to be varied in accordance with said condition, means operable to control the pressure in said control line independentLv of said condition responsive device for causing said controller to be positioned at least a predetermined distance from one limit of its movement and valve means for preventing the pressure exerted upon said motor means by said last mentioned means from affecting said condition responsive device.

4.111 a pneumatic control system, in combination, a controller movable from one position to another, pressure actuated motor means for said controller operable to position said controller in accordance with the pressure applied to said motonmeans through a control line, a condition responsivedevice for varying the pressure in said control line upon change in value oi the condition to which said device is responsive to thereby cause the position 01 said controller to vary in accordance with said condition, and means for normally preventing the pressure in said control line from varying beyond the value necessary ior causing said controller to be positioned at least a predetermined distance from one limit of its movement.

5. In a pneumatic control system, in combination, a controller movable from oneposition to another, pressure actuated motor means for-said controller operable to position said controller in accordance with the pressure exerted upon said motor means, a condition responsive device ior applying varying pressures upon said motor means for different values of the condition to which said device is responsive to thereby cause the position-of said controller to be varied upon change invalue of said condition, meansfor controlling the pressure applied to said motor means for causing said motor means to position saidcontroller at least a predetermined distance from one limit" of its movement, and means controlled by said condition responsive means fox-controlling said pressure controlling means. F

6. In a pneumatic control system, in combination, a controller movable from one position to another, pressure actuated motor means fol-said controller operable to position said controller in accordance'with the pressure exerted upon said motor means, a condition responsive device for applying varying pressures upon said.- motor means for different values of the condition to which said device is responsive to thereby cause the position of saidcontroller to .be variedv upon change in value of said condition, and means controlled by said condition responsive device for normally rendering said condition responsive device inoperative to vary the'pressure applied .to

said motor meansbeyond a predetermined value;

I. In an air conditioning system,-in combination, a conditioning chamber, means for causingair toibe conditioned to flow through said conditioning chamber, a condition changerin said conditioning chamber for changing the'condi tion of the air as it flows therethrough, means including a damper-for supplying ireshairto' said-conditioning chamber and for controlling the flow of said fresh air, pressure actuatedj mo tor means for controlling said damper, other pressure actuated motor means ion-controlling" the condition changer, said motor means being arranged so that an equal change in pressure applied to both of said motor means has a different effect upon one motor means than upon the other, condition responsive means for varying .the pressure applied to both motor means and applying equal pressures to both motor means, means for normally preventing said condition responsive device from varying the pressure applied to the damper motor means beyond a predetermined value to maintain .a minimum opening of saidiresh air damper, and means for placing said last named means into or out of operation.

8. In an air conditioning system, in combination, means for supplying fresh air to a space, damper means for controlling the fresh air supply, pressure actuated motor means for positioning said damper means, said motor means being actuated by pressure fluid applied thereto through a control line, a condition responsive device for varying the pressure in said control line upon change in value of the condition to which it responds to thereby position said damper means in accordance with the value of said condition,

'and means for normally preventing said condition responsive device from varying the pressure in said control line beyond the value necessary for causing said fresh air damper to assume a predetermined minimum flow position, for thereby maintaining at least a predetermined flow oftreshairtosaidspace.

9. In an air conditioning system, in combination, means for supplying fresh air to a space, damper means for controlling the fresh air supply, pressure actuated motor means for positioning said damper means, said motor means being actuated by pressure fluid applied thereto through a control line, said motor means comprising a chamber having a movable wall adapted for movement in response to change in pressure applied thereto, a condition responsive device for varying the pressure in said chamber upon change in value of the condition to which it respondslao thereby position said damper means in accordance with the value of said condition, and means for normally preventing said condition responsive device from varying the pressure in said chamber beyond the value necessary for causing said fresh air damper to assume a predetermined minimum flow position, for thereby maintaining at least a predetermined minimum fiow of fresh air to said space.

10. In men conditioning system, in combination, means for supplying fresh air to a space, damper means for controlling the fresh air supply, pressure actuated motor means ior positioning said dampermeans, said motor means being actuated by pressure fluid applied thereto through a control line, said motor means comprisinga chamber having a movable wall adapted for movement inresponse to change in pressure applied thereto, a condition responsive device tor varying the pressure in said chamber change in value of the condition to which it responds to thereby position said damper means in accordance with the value of said condition, and means for supplying pressure to said chamber independently oisaid condition responsive means, said last'recited means supplying the necessary pressure to said chamber to maintain said damper in at least a predetermined minimum flow position.

11.121 a system oi the class described, in combination, a control device movable from one position to another, a single motor ior actuating said control device, means including a first control means actuated by a condition responsive device sume a position intermediate its range of movement and at least a predetermined distance from one limit of its range 01' movement independently of said first control means, and means actuated when said first control means causes movement of said motor beyond said predetermined distance for disconnecting said second control means from said motor to thereby place said first control means in control or said motor without lnterierence from said second control means.

12. In a system of the class described, in combination, a control device movable irom one position to another, a single motor for actuating said control device, means including a first control means actuated by a condition responsive device and constructed and arranged ior graduatingly positioning said motor in accordance with variations in the condition to which said condition responsive device responds, means includ ing a second control means for also controlling said motor, said last mentioned means being constructed and arranged to cause said motor to assume a position intermediate its range of movement and at least a predetermined distance from one limit of its range 01' movement independently of said first control means, and means disconnecting said first control means from the motor and connecting the second control means thereto when the condition to which the condition responsive means responds varies to one side of a predetermined value and for disconnecting said second control means from the motor and connecting the first control means thereto when said condition varies tothe other side of said predetermined value.

FRANK C. GIBBS. KARL FIGENBAUM. 

